The present invention relates to a pulse oscillating gas laser device such as an excimer laser device.
In a pulse oscillating gas laser device such as an excimer laser device, it is conventionally known that shock waves and acoustic waves (hereinafter, generally referred to as shock waves) occur on the occasion of pulse discharge. Due to the shock waves, fluctuations occur to the density of a laser gas, and a beam profile, energy, and wavelength of laser light become unstable. The art of preventing this is disclosed in, for example, Japanese Patent Application Laid-open No. 4-328889. FIG. 17 shows a detail view of an area near discharge electrodes of an excimer laser device 11 disclosed in Japanese Patent Application Laid-open No. 4-328889, and a prior art will be explained hereinafter based on FIG. 17.
In FIG. 17, meal discharge electrodes 14 and 15 are placed to oppose each other inside a laser chamber 12 in which a laser gas is sealed. An upper cathode 15 is fixed to a cathode base 36 with insulating properties, and the cathode base 36 is fixed to the laser chamber 12. A lower anode 14 is mounted on an anode base 40 electrically connected to the laser chamber 12. The cathode 15 is electrically connected to a high voltage side HV of a high-voltage power source 23, and the anode 14 and the laser chamber 12 are electrically connected to a grounding side GND of the high-voltage power source 23. High voltage is applied between the discharge electrodes 14 and 15 from the high-voltage power source 23 to cause a primary discharge in a pulse form in a discharge space 37, thereby causing laser light in the pulse form.
In this situation, a shock wave 41 occurs from the discharge space 37 as a result of the primary discharge. The shock wave 41 is reflected at components in the vicinity of the discharge electrodes 14 and 15, and is returned to the discharge space 37, whereby the density of a laser gas in the discharge space 37 fluctuates. As a result, the primary discharge becomes unstable, and the beam profile, energy stability, and wavelength stability of the laser light are disturbed. In order to prevent this, in the aforementioned Japanese Patent Application Laid-open No. 4-328889, porous ceramics 46 and 46 are fixed on the cathode base 36 and the anode base 40, respectively. The porous ceramics 46 and 46 as described above absorb the shock wave 41 and prevent the shock wave 41 from returning to the discharge space 37.
However, the aforementioned prior art has the disadvantages as described below.
Specifically, in FIG. 17, the cathode 15 and the laser chamber 12 are electrically insulated from each other, and on the occasion of primary discharge, a large potential difference occurs between them. Thus, creeping discharge sometimes occurs between the cathode 15 and the laser chamber 12 via the surface of the porous ceramic 46. As a result, primary discharge is not carried out favorably, thus causing the disadvantages that the output of laser light is reduced and in an extreme instance, laser light is not generated. In order to avoid creeping discharge, it is advisable to make a distance between the cathode 15 and the laser chamber 12 longer, but this makes the excimer laser device 11 larger.
To prevent creeping discharge, the art of providing projections and depressions on the cathode base 36 to form a rib portion is known. According to this, the insulation distance between the cathode 15 and the laser chamber 12 is lengthened, and creeping discharge hardly occurs.
Further, in view of the demand for increase in the repetition frequency of laser oscillation in recent years, the need for reducing inductance of primary discharge arises. For this purpose, it is necessary to reduce an area of a current loop formed by a return plate (not shown) for electrically connecting the cathode 15 and the anode 14, and the anode 14 and the laser chamber 12. As a result, the distance between the cathode 15 and the laser chamber 12 is shortened, and the creeping discharge between the cathode 15 and the laser chamber 12 easily occurs. The aforementioned rib portions are also necessary to prevent this.
However, the phenomenon, in which shock waves 41 generating from the discharge space 37 enter the recessed portions of the rib portion and are reflected toward the discharge space 37 at a high reflectivity, sometimes occurs. Thus, there arises the disadvantage that the shock waves 41 make the beam profile, energy, and wavelength unstable as described above.
The present invention is made in view of the above-described disadvantages, and its object is to provide a pulse oscillating gas laser device which can reduce effects of shock waves caused by primary discharge and perform stable laser oscillation.
In order to attain the above-described object, a pulse oscillating gas laser of the present invention is a pulse oscillating gas laser device for exciting a laser gas by causing primary discharge in a pulse form between a pair of discharge electrodes opposing each other and oscillating laser light, and has the constitution in which
a rib portion with insulating properties for preventing creeping discharge is provided on a cathode base with insulating properties, to which the discharge electrode at a high voltage side of a pair of the discharge electrodes is fixed, and
a damping material for attenuating shock waves caused by the primary discharge is inserted in an inside of a groove portion between a raised portion of the rib portion and the high-voltage side discharge electrode.
According to the above constitution, the shock waves are attenuated favorably, and the rib portion with insulation properties makes it possible to prevent creeping discharge.
Further, in the pulse oscillating gas laser device,
the damping material may be inserted into a recessed portion of the rib portion.
According to the above constitution, the shock waves emitted to a distance from the discharge electrodes are also attenuated, and therefore the effect of the shock wave is reduced.
Furthermore, in the pulse oscillating gas laser device,
the damping material may be in close contact with a side face of the raised portion and a side face of the high-voltage side discharge electrode, and may be formed into a U-shape.
According to the above constitution, the shock waves reflected at the surface of the damping material can be also prevented from returning to the discharge space, and the shock waves can be attenuated at high efficiency.
Still further, in the pulse oscillating gas laser device, the damping material may be provided in close contact with the discharge electrode at a grounding side of a pair of the discharge electrodes.
According to the above constitution, the shock waves emitted toward both of the high-voltage side and grounding side are attenuated, and therefore the effect of the shock waves can be reduced.
Further, in the pulse oscillating gas laser device,
the damping material is a porous material with porosity of not less than 90%.
According to the above constitution, the porous material with high porosity is used, thus making it possible to attenuate the shock waves more efficiently.